High critical temperature in a superlattice of quantum wires

Here the authors report experimental evidence that the high Tc superconductivity in a cuprate perovskite occurs in a superlattice of Josephson coupled quantum wires. They show that this particular heterostructure provides the physical mechanism raising Tc from the low temperature range Tc < 23K to the high temperature range 30K<Tc < 150K by amplification of the critical temperature of the homogeneous CuO2 plane by a factor ∼10. The structure of the high Tc superconducting CuO2 plane in Bi2Sr2CaCu2O8+y (Bi2212) at the mesoscopic level (10-100 angstrom) has been determined. The superconducting plane is decorated by a plurality of parallel superconducting stripes of width L defined by the domain walls formed by stripes of width W characterized by a short Cu-O(apical) distance and large tilting ∼10 degrees of the distorted square pyramids. The authors have measured the width of the domain walls W=±1 angstrom and of the stripes L = 14 ± 1 angstrom. The critical parameters raising Tc are: (1) the Fermi level is near the bottom of the second subband of the stripes, with k2y = 2π/L, formed by the quantum size effect and (2) W is of the order of the superconducting coherence length ξ0